History of Windmills

The Persians seem to have been the first to develop windmills (between 500 and 900 A.D.). Sails had long been used to move ships at sea, but the Persians converted the wind for use in grinding grain. These were vertical style mills with the sails spinning the shaft directly connected to a grind-stone or pump. Windmills first appeared in Europe about the time of the Crusades (1096-1270). As the design is considerably different from the Persian model there is much speculation on whether they were developed independently or borrowed by some Crusaders returning home who might have seen them in operation. The first known windmill in China is documented in 1219 A.D. It was a grain grinding mill.

The earliest windmills in Europe had a post-mill structure. The name is derived from the fact that the main structure sits on a post, usually a wooden post, that allows the entire structure to turn to face the wind. The post-mill could not face the wind on its own. It was turned by a long beam attached horizontally to the body of the mill. The mills generally sat upon a tripod structure composed of two crossed beams resting on the ground and four angled beams coming up to support the post in the center. These windmills had a horizontal axis, so the sails could take better advantage of the wind. The power was transferred to machines by cogs and gears.

Later smock mills were developed that allowed just the top part of the windmill to be turned to face the wind. This was a vast improvement as it was lighter and easier to turn. More permanent structures could then be built to house the mill. Brick and stone tower mills developed from this innovation.

In the late 1300s the Dutch took windmill technology to new heights, developing new sail designs that increased efficiency, including using a leading edge on the sail to create aerodynamic lift.1 Sails were generally of cloth and stretched over a wooden frame. In some designs these sails could be trimmed to take advantage of variable wind conditions. The large windmills of the Dutch design continued in use all across Europe until the advent of the steam engine in the 1800s. The English added a fantail to some windmills that allowed them to be turned using wind power.

In the United States in the mid 1800s a new style of windmill was developed that comprised a small rotor set on top of a skeletal steel structure. At first these were used a few wooden blades, but soon became more technologically advanced, using steel blades that would fold back in very high winds to avoid damage to blades and any connected equipment. These were used primarily in the American West as water pumps to draw up water for cattle or crop irrigation.

The next step was to develop rotors that looked like airplane propellers. These were connected to small generators and provided electricity in rural areas. The problem with wind generated power is that it is subject to the whimsies of the wind. Though handy for running direct current appliances, when electrification by connection to the main power grid came to many rural areas of the United States during the 1930s, the windmill lost its popularity.

With the increasing interest in clean energy and advances in technology, windmills have come back into vogue.